Field of the Invention
The present invention relates to a vibrator that is the driving source of an ultrasonic motor used for a lens barrel or the like of an image capturing apparatus and an ultrasonic motor using the same.
Description of the Related Art
As the characteristic features of an ultrasonic motor using the ultrasonic vibration of a piezoelectric element, it can obtain a large driving force with a small body, cope with a wide speed range, and reduce the vibration and noise. Especially, as the characteristic features of a method using a chip type vibrator formed by bonding a piezoelectric element and an elastic member, the vibrator is relatively small, and a driven member can be not only rotatably driven but also linearly driven. For this reason, an ultrasonic motor using a chip type vibrator is suitable as an actuator for linearly driving a lens in the lens barrel or the like of a camera that needs a small motor with a large driving force. A device disclosed in Japanese Patent Application Laid-Open No. 2009-124791 is an example of an ultrasonic motor using a chip type vibrator.
In this method, a standing wave vibration is excited in the vibrator using expansion and contraction of the piezoelectric element when a voltage is applied to the piezoelectric element. The standing wave vibration excited in the vibrator is transmitted to the driven member, thereby driving the driven member. To drive the ultrasonic motor, it is necessary to apply a voltage to one or more pairs of electrodes provided on the piezoelectric element. Hence, the vibrator actually includes a conducting member as a line used to apply a voltage from an external feed means to the piezoelectric element.
In the vibrator described in Japanese Patent Application Laid-Open No. 2009-124791, one electrode of an electrode pair is extended to the same surface as the other electrode via a through hole, thereby gathering the plurality of electrodes to one surface. The conducting member is, for example, a flexible substrate, which is bonded to a wide surface on which the plurality of electrodes are gathered, thereby simultaneously supplying power from an external feed means to the plurality of electrodes. At this time, the adhesive portion between the piezoelectric element and the conducting member has a sufficiently large adhesive force because a large adhesion area can be obtained.
However, if one electrode is extended to the other electrode, as in the vibrator described in Japanese Patent Application Laid-Open No. 2009-124791, the region occupied by the extended electrode becomes an inactive region, and no driving force is generated. When the vibrator is downsized, the ratio of the inactive region increases, and a sufficient driving force cannot be obtained. For this reason, when downsizing the vibrator, it is necessary to adhere part of the conducting member to each of the plurality of electrodes on the piezoelectric element to attain conduction without extending the electrode so as not to form an inactive region. Additionally, in the vibrator described in Japanese Patent Application Laid-Open No. 2009-124791, one electrode is covered with an elastic member. Hence, conduction to the electrode covered with the elastic member needs to be attained via the elastic member.
In the small chip type vibrator as described above, it is difficult to obtain a sufficiently large adhesion area in the adhesive portion because the surface area of the vibrator is small. In addition, since the electrodes on the piezoelectric element are very thin, it is also difficult to perform a process of increasing the adhesive force by, for example, roughening the surface. Hence, when the adhesion area is small, a sufficiently large adhesive force cannot be obtained in the adhesive portion between the piezoelectric element and the conducting member. Under these circumstances, if an unintended large external force is generated in the conducting member upon assembling the ultrasonic motor, a force more than the adhesive force may act on the adhesive portion between the piezoelectric element and the conducting member, and the conducting member may peel off.